1. Field of the Invention
The present invention relates to an imaging apparatus, and more particularly, to an imaging apparatus and imaging system provided with autofocus functions, a method for controlling the same, and a program that causes a computer to execute the method.
2. Description of the Related Art
Recently, imaging apparatus such as digital still cameras and digital video cameras (camcorders, for example) are becoming popular. Such imaging apparatus image a person, animal, or other subject to generate picture data (an imaged picture), and record this picture data as picture content. There also exist imaging apparatus that display an imaged picture generated by an imaging element on a display unit as a live preview picture while in an imaging standby state in the case of shooting a still picture, for example. By displaying a live preview picture in this way, the user is able to easily confirm his or her desired angle of view and composition before shooting.
Also, imaging apparatus provided with autofocus functions that automatically focus a subject are becoming widely popular. A contrast-detecting autofocus function (referred to as contrast AF (Auto Focus)) exists as one example of such autofocus functions.
With contrast AF, high-frequency components in the spatial frequency of a picture are extracted in a specific region (AF region) of an imaged picture, and focus control is conducted by moving a focus lens to a position that maximizes a luminous intensity difference in the extracted high-frequency components. Also, with contrast AF, a given focus lens movement range is set, and by moving a focus lens within this range, subjects are successively acquired and focus control is conducted.
Herein, in the case where focus control is conducted on a moving subject, a focus lens movement range should be set according to the subject's movement in order to acquire the moving subject. For example, there have been proposed imaging apparatus that set a focus lens movement range for a moving subject while predicting that subject's movement velocity.
For example, there has been proposed an imaging apparatus that sets a subsequent focus lens movement range on the basis of respective rating values calculated at a plurality of positions given by movement of a focus lens within a given range in a first period and the rating value variation (see Japanese Unexamined Patent Application Publication No. 2010-8695, FIG. 11, for example). This imaging apparatus calculates respective rating values computed during a first period, and a rating value (second rating value) at one of a plurality of positions within a given range during a period (second period) lasting until a focus position based on those respective rating values is computed. Then, the imaging apparatus calculates the rating value variation on the basis of the second rating value and a rating value (computed in the first period) corresponding to the position of the second rating value, and sets the next focus lens movement range on the basis of a focus position based on the respective rating values in the first period and the rating value variation.